Modern motor vehicles have an internal combustion engine which is operated with a fuel (e.g. gasoline or diesel) stored in a tank. Owing to the temperatures and pressures prevailing in the tank, gases are formed by evaporation, and these must not be released into the environment of the vehicle or may be released to only a limited extent. On the one hand, there are legal limits for evaporative emissions, and these are determined in defined cycles, and, on the other hand, discharged gas containing hydrocarbons (HC) leads to a perceptible fuel odor. This odor is perceived to be troublesome by customers and thus leads to customer complaints. Moreover, a fire hazard can also arise from escaping gas or liquid fuel in extreme cases.
To avoid releasing the hydrocarbon-enriched gas formed into the environment, it is stored temporarily in an activated carbon filter. To avoid overflow from the activated carbon filter, the filter must be purged as often as possible during operation. At the same time, the purging rate must be higher on average than the volume of gas formed in the tank. The activated carbon filter is purged by feeding the tank venting gas into the air supply to the internal combustion engine. The fuel present in this gas is allowed for in the pilot control of the mixture by the control unit of the internal combustion engine, ensuring that the fuel gases formed in the tank are burnt with neutral effects on combustion and emissions. To produce purging of the activated carbon filter, a purging gradient (pressure gradient) must be achieved. This necessary purging gradient is produced by a vacuum in the air supply to the internal combustion engine relative to the ambient pressure of the vehicle by means of a throttle element, e.g. a throttle valve. Control of venting is accomplished by means of a valve, which is usually controlled electrically.
In the case of supercharged internal combustion engines, e.g. those having a turbocharger or a supercharger, there is an excess pressure in the intake system in the upper load range of the internal combustion engine, i.e. at full load or in upper partial load ranges, with the result that it is not possible to achieve purging of the activated carbon filter at these operating points. In order to be able to perform purging of the activated carbon filter in the supercharged mode of the internal combustion engine, the proposal in the prior art is to arrange the point of introduction of the tank venting gas ahead of the compressor of the turbocharger. If there is an insufficient vacuum in the intake line ahead of the compressor, tank venting can be improved by means of a Venturi nozzle. For this purpose, an ejector jet path is installed, starting from the high-pressure side and leading to the low-pressure side of the compressor. A passive ejector pump (Venturi nozzle) is integrated into this ejector jet path and produces the required vacuum for the tank venting system in the supercharged mode of the internal combustion engine.
However, supercharged internal combustion engines have the disadvantage that when there is a rapid reduction in load, there can be “pumping” of the compressor. This state arises when, in the event of a reduction in load, the throttle valve is rapidly closed and the air column builds up as far as the compressor counter to the direction of flow of the air path. As a result, there is a pressure increase in the region of the intake tract between the compressor and the inlet valves of the internal combustion engine and consequently a flow separation in the compressor, which has a negative acoustic effect.
To avoid compressor pumping and component damage resulting therefrom, overrun air recirculation valves are used in the prior art. These are integrated into the region of the intake tract between the compressor and the throttle valve of the internal combustion engine in order to rapidly dissipate the existing excess pressure in the high-pressure section of the intake tract in the direction of the low-pressure side of the intake tract when there is a reduction in load, i.e. the high-pressure side of the compressor is connected gas-conductively to the low-pressure side of the compressor.
The use of overrun air recirculation valves entails additional hardware, which generates additional expenditure in the development and assembly of internal combustion engines. Moreover, there is the risk with all the additional components that they will fail in operation and consequently may cause loss of comfort or consequent damage to other components.
To circumvent this disadvantage, German Patent DE 10 2011 084 539 B3 proposes a turbocharger having a compressor, the housing of which contains a low-pressure inlet region connected to a low-pressure inlet and a high-pressure outlet region connected to a high-pressure outlet. The low-pressure inlet region is connected to the low-pressure side of an intake pipe and the high-pressure outlet region is connected to the high-pressure side of the intake pipe. The compressor has a Venturi nozzle, which is arranged between the high-pressure outlet region and the low-pressure inlet region and is furthermore connected to an activated carbon filter to allow venting of the latter. The compressor furthermore has an overrun air recirculation valve, to which the Venturi nozzle is connected, and venting of the activated carbon filter takes place when the overrun air recirculation valve is opened.
However, the disadvantage with this known embodiment is that tank venting requires a significantly smaller flow cross section than an overrun air recirculation valve.
It is an object of the embodiments of the present invention to indicate a measure with which the abovementioned disadvantages can be avoided while simultaneously reducing the components used.
This object is achieved by the features in the characterizing part of patent claim 1.
Combining two functions in a valve combination eliminates the duplicated gas supply and gas discharge lines to and from the valves, the second control cable for the valves and a second component holder for a second housing. Advantages thus arise in terms of costs, installation space and weight without functional disadvantages.
Thus, according to patent claim 2, the overrun air recirculation valve and the tank venting valve are preferably arranged in a common housing in order to save installation space.
According to patent claim 3, the tank venting valve may include a robust Venturi nozzle and a likewise known flow widening valve having at least two flow cross section widening stages.
In another preferred embodiment, according to patent claim 4, the fuel tank can have a gas connection to the intake tract by means of the valve, thereby allowing purging of the activated filter when the internal combustion engine is operated in the unsupercharged mode (naturally aspirated mode).
According to patent claim 5, a first throttle element, by means of which the tank venting valve can be shut off in order to minimize leakage losses and thus power losses of the internal combustion engine, is preferably provided in the first or second line.
The embodiments of the invention are explained in greater detail below by means of a schematically illustrated embodiment example in a single FIGURE.
Other objects, advantages and novel features of the embodiments of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.